Numerous aromatic polyisocyanates containing more than two isocyanate groups per molecule are known. It is also known that such polyisocyanates are potentially suitable as starting materials for the preparation of adhesives. Representatives of this class of compounds which have achieved a position of technical importance are described, for example, in Kunststoff Handbuch, Vol. 7: Polyurethane, published by G. Oertel, 2nd Edition, Hanser Verlag, Munich 1983, pages 13 to 15 and 581 to 596. The following are typical examples of such polyisocyanates: Tris-(4-isocyanatophenyl methane, polymer-diisocyanatodiphenylmethane, thiophosphoric acid tris-(p-isocyanatophenylester), the adduct of trimethylolpropane and 2,4-diisocyanatotoluen, etc. Thiophosphoric acid tris-(p-isocyanatophenyl)-ester is particularly distinguished by its good adhesive properties on various types of rubber as well as being virtually colorless and is therefore widely used as adhesive for sensitive, light colored materials.
Although the known polyisocyanates have reached a high level of quality in their adhesive properties, further improvements are desirable in view of the higher standards demanded, especially with regard to the heat resistance and compatibility with solvent-containing adhesives based on natural rubber and polychloroprene.
It is therefore an object of the present invention to provide new polyisocyanates which have such improved properties.